Circular features are often used as locating datums in manufacturing. Such features can be accurately produced with relative ease, and can be used to determine the position and orientation of parts. Part location is critical during machining since often a part must be removed from a machine and repositioned on the machine for subsequent machining operations. If part orientation is not precisely known, it is very difficult to accurately mate and assemble parts.
Laser scanning is a technique which is being used for capturing the geometry of engine parts such as combustion chambers, intake and exhaust ports. These features are complex free-form shapes and require many measurements to accurately describe them. Determining the true position of these free form surfaces in the overall cylinder head can be quite difficult.
A coordinate measuring machine (CMM) is used to measure a part, and reference features are measured to establish the coordinate system for measuring other features of interest. However, CMM is mainly used for inspection of known parts and not for capture of free form geometry. CMM machines typically have algorithms to find features such as holes or edges from user supplied nominal locations. The process, however, is slow, interactive and operator intensive. In comparison, laser scanning is not highly interactive but it requires feature determination off-line through statistical processing.